The centrifugal blower units of this kind have an axial intake region through which air is sucked into the spiral housing of the blower. In the blower, the air is accelerated by the rotating fan wheel and finally blown out in a tangential direction from the spiral housing.
In the prior art, the problem is known that blowers produce high noise emissions and there is a constant desire to reduce the noise emissions specifically in motor vehicles with the least possible technical expense. Noise reduction plays a role in regard to comfort and in regard to safety, since external and internal acoustic warning signals need to be noticed by the driver.
From KR 10-2006-0117012 A, there is known a spiral housing for a centrifugal blower unit in which the housing is formed specially on the intake opening in the axial direction in order to reduce the flow noises of the blower unit. By means of a diaphragm or the shape of the housing edge itself, the edge is tilted in the axial direction toward the fan wheel at the intake region. The resulting annular bulge reduces the noise emission.
Another approach to the solution of the problem of too high flow noises of the blower unit was chosen in JPU 1981-171699. Here, the spiral housing of the centrifugal blower unit was outfitted with a radial diaphragm immediately above the fan wheel, which unlike the previously mentioned design is not tilted in the flow direction, but instead disposed at a right angle to the fan axis.
A different design approach is taken by U.S. Pat. No. 6,299,409 B1, which provides a bell mouth region at the top of the spiral housing of the centrifugal blower unit. The bell mouth region is part of the spiral housing and borders the flow inlet region. Furthermore, the bell mouth region corresponds on the inside to the shape of the fan wheel and optimizes the air flow processes by preventing secondary currents. Thanks to this approach, secondary noise due to the formation of secondary currents has been substantially reduced by means of the bell mouth region.
The problem solutions of the prior art are distinguished in that individual aspects have been achieved in regard to improving the flow characteristics and the attendant noise development, but no truly satisfactory solution to the problem has been found.